More information on George Woltman can be found through his autobiography at http://www.utm.edu/research/primes/bios/titans/Woltman.html.

Even before starting the GIMPS project, he was one of the first people searching for prime numbers on a workstation. He has contributed to other prime number searches as well; among other things, he has written the program PRP, which can speed up a search using Yves Gallot's program Proth.exe by a factor of two or three. Woltman, with the help of PC users across the Internet, has discovered THE 4 largest presently known prime numbers, and there is a better than even chance that another will be discovered in 2000 or 2001.

I have personally spoken with Woltman on the official GIMPS mailing list, and have found him extremely responsive to bug reports, even those purely cosmetic in nature, far more than many free software developers.